


Hi there,
inspired by the pin matrix in EMS Synthis, I'm working on a MIDI controlled matrix mixer. Unlike the (unmodified) EMS matrix, this one is fully buffered and true summing, meaning that audio signals and CVs are added up correctly. Also this is not just a crosspoint switch as in some existing devices, here one can route any input signal to any output at the same time.
I have a first set of 8x10cm PCBs that hold the mixing fabric and which allow for a 16x16 matrix when fully populated. currently I soldered the components for a 4x4 matrix and this seems to work so far. I also have the PCB layout ready for a 5x5cm sized 8x8 matrix which I have not fabbed yet. a second PCB will hold the digital part with MIDI in and whatever other UI functions. currently this is just a small STM32 dev board wired in.
The 16x16 matrix could even fit inside an EMS Synthi right behind the real matrix or it could be wired in via the Prestopatch connector for a MIDI-fied Synthi - though I am sure that's pretty close to heresy

The switch fabric PCB is all SMT with SO and TSSOP components and resistors down to 0402, it can be soldered by hand though I had help from a stereo microscope to do so.
my current test setup looks like this:

and here is an example of summing the first four fourier components of a square wave - 4th input signal not shown as I don't have a 5-channel scope


besides the 8 input and 8 output jacks I want to put an LED push buttons for each input and output. Holding down one input button would light up the LEDs on the output side, showing to which output channel this input is routed to. Pressing an output button while still holding down the input button would them toggle this connection, allowing to change the routing. same for holding down an output button, it would show what inputs are routed to that output and allow to toggle each state.
input and output channels could also be muted by a double click on the respective button and blinking the LED to indicate muted state.
I have not decided yet on what control signals I will put, MIDI, USB host/device and or RS232 control, currently I am switching manually through the debug UART on the CPU board.
Regards,
Vladimir